Chickens are seen at a livestock market before in Kunming, Yunnan province, China February 22, 2017. Stringer/File Photo

A new strain of bird flu could soon provoke a global crisis. The disease has infected 1,400 people in China -- and killed 40 percent of them. Experts worry the virus could spread worldwide. A few cases have already been detected in Tennessee.

Avian flu is one of hundreds of deadly diseases transferred between animals and humans. Every year, these "zoonotic" diseases kill about 2.7 million people - roughly the population of Chicago.

Public health officials won't be able to defeat these ailments solely by inoculating and treating people. They'll need to combat them at the source -- the animals that spread viruses and bacteria. Zoonotic diseases illustrate just how interconnected animal and human health are. Safeguarding human health thus requires paying close attention to animal health, too.

Countries around the world are urbanizing and expanding into formerly rural areas. Consequently, people are coming into more frequent contact with animals and the pathogens they carry. Zoonotic disease already account for 75 percent of emerging diseases. As human-animal interactions increase, those diseases will become more prevalent and more deadly.

Consider just a few recent outbreaks. A recent Ebola flare-up in the Democratic Republic of the Congo infected about 50 people and killed 29. A few years ago, a global outbreak of the disease, which originates in chimps and other primates, killed more than 11,000 people, mostly in West Africa.

Brazil is coping with an outbreak of yellow fever, which mosquitoes spread to humans. For most people, the disease causes fever, chills, and body aches. Many develop severe symptoms like internal bleeding, organ failure, and shock. Since July 2017, the disease has infected more than 1,100 in Brazil and killed over 300. Health officials worry yellow fever could spread to the United States, since Florida is a popular tourist destination for people from South and Central America.

West Nile virus - which causes headaches, diarrhea, vomiting, and in extreme cases, death - has already arrived in the United States. The mosquito-borne disease has started popping up about a month earlier than it did last year, when more than 2,000 people contracted it.

China bird flu
Health officers cull poultry at a wholesale market, as trade in live poultry suspended after a spot check at a local street market revealed the presence of H7N9 bird flu virus, in Hong Kong June 7, 2016. Bobby Yip

Tackling zoonotic diseases requires acknowledging the interplay among the health of humans, animals, and the environment - an approach known in the medical community as "One Health." Experts from all three fields must collaborate to address the challenges that zoonoses pose.

The term One Health was coined relatively recently, but it has been the guiding spirit of history's most effective responses to epidemics.

Take smallpox. In the 18th century, a physician and farmer observed that people who interacted frequently with cows were less likely to develop smallpox. Researchers later realized that people who contracted cowpox - a relatively harmless virus humans catch while milking cows - did not get smallpox. That discovery led to a vaccine against the disease, which was eradicated worldwide in the 1970s.

In July, the Food and Drug Administration approved the first drug to treat smallpox in the event of a bioterrorist attack. The medicine resulted from years of collaboration between microbiologists, physicians, and public health experts.

Other successful One Health-influenced campaigns abound. In Thailand, farmers and health officers are using an app to share suspicious human and animal illnesses with the Ministry of Public Health. To prevent Rift Valley fever in East Africa, scientists from the U.S. Centers for Disease Control and Prevention work with veterinarians and farmers to vaccinate sheep and cattle to stop them from infecting people.

There are even applications for One Health in more domesticated settings. A growing body of research shows that pets can boost humans' mental and physical health. So healthcare professionals are increasingly incorporating pets as modes of therapy for all sorts of physical and mental ailments.

Many universities are invested in One Health, too. The philosophy is at the heart of our medical and veterinary curricula at St. George's University in Grenada, where I teach.

Veterinary schools have tended to more forcefully champion One Health. Given the impact that animal health can have on human health, medical schools ought to make the approach more of a curricular priority.

Avian flu and other zoonotic diseases pose a grave threat to people around the globe. A One Health approach is the best way to combat these menaces.

Satesh Bidaisee is a professor of public health and preventative medicine and assistant dean for graduate studies at St. George's University in Grenada.